This invention relates to methods for displaying signal measurements within multiple ranges of a parameter, and particularly though not exclusively to methods for displaying spectral power measurements.
Telecommunications equipment such as mobile telephones and cellular telephone base station transceivers are subject to a variety of checks and tests during manufacture to ensure that they are operating correctly and in conformity with applicable standards and regulations. One such test is the adjacent channel power (ACP) measurement, which measures the signal power levels in frequency channels that are adjacent to the transmission carrier or carriers (the reference carrier(s)) on which the equipment is intended to transmit. The ACP measurement typically uses a spectrum analyzer and involves sweeping through a range of frequencies around on the reference carrier, and determining the signal power at multiple points within a band centred on the carrier and containing the intended signal, and within adjacent bands offset either side of the carrier band. There may be for example six adjacent bands of each side of the carrier. The centre frequency and bandwidth of the carrier band and each adjacent band are usually specified in the relevant standard or regulation.
Conventionally the result of an ACP measurement has been presented as a graphical display of the signal spectrum (power versus frequency) within the overall frequency range of the measurement, as shown in FIG. 1. The upper and lower frequencies of the carrier band and of the offset bands are marked on the display, and the signal power within each band is indicated numerically adjacent the graphical display, e.g. beneath it. This approach leads to a very cluttered display, especially for larger numbers of adjacent bands, and can be extremely unintuitive and misleading in the case where the adjacent bands overlap. Associating frequency offsets with the respective calculated results is time-consuming and prone to error, as these items are located in separate areas of the display.
Another approach to the display of ACP measurements is to use a bar graph display which displays the carrier and each offset band as a respective one of several equal-width vertical bars, the height of the bars being indicative of the amplitude of the measured powers, as shown in FIG. 2. It is very difficult to adjust the analyser settings with this display, as there is virtually no visual feedback which would enable checks to be made of aspects such as correct relationship of frequency settings and absence of unintended channel overlap. The display is also readily but often incorrectly interpreted as indicating that all offset bands are of equivalent span and spacing.
According to one aspect of this invention there is provided a method of generating a display of a signal measurement within each of multiple ranges of a parameter (such as frequency), comprising the steps of:
obtaining measurements of a signal within each one of multiple ranges of a parameter;
deriving for each of said multiple ranges of the parameter:
a representative measurement value and
an extent of the range;
defining a respective graphical display element for each of said multiple ranges of the parameter, a first dimension of each display element being indicative of the representative measurement value for the respective range of the parameter, and a second dimension of the display element being indicative of the extent of that respective range of the parameter; and
generating a display of the measured signal throughout the multiple ranges of the parameter, with the graphical display elements superimposed at positions corresponding to the respective ranges of the parameter.
Thus in the case of an adjacent power measurement, the display may comprise a trace of the measured signal power throughout frequency channels adjacent a reference (carrier) channel, with a vertical bar superimposed for each adjacent frequency channel, each bar having a width corresponding to the bandwidth of the respective adjacent channel and a height indicative of the power measured within that channel.
If desired the measurement value for each channel may also be indicated numerically in proximity to that channel, for example above it.